• Adds to JWT, KeyAuth, CSRF support for multivalue extractor - This is mostly useful with headers but this PR adds this other variants also. Usecase - You are using JWT middleware and expect Authentication header with value Bearer xxxx but your intracture has upstream proxy that adds Basic authentication also. Now even if you fill basic auth in browser and your application sends requests with JWT token you would be in trouble as previously JWT middleware knows only to extract first Authentication header value - which could be JWT token but could be also Basic Auth. This change allows extractor to return all those header values and run JWT token checks or validation for Keyauth on them.
• Add flag NoErrorContinuesExecution to JWT and KeyAuth middleware to allow continuing execution next(c) when error handler decides to swallow the error (returns nil). Usecase: This is useful in cases when portion of your site/api is publicly accessible and has extra features for authorized users. In that case you can use ErrorHandlerWithContext to set default public JWT token value to request and continue with handler chain. Note: this is similar to Allow JWT middleware to gracefully fail #2048

p.s. there are ugly error handling parts just to preserve similar/same errors that those middlewares previously returned. Unfortunately all these 3 are quite inconsistent how they do error handling - JWT has 2 generic types. Keyauth has specific error values.